Tilting breech bolt lock actuating mechanism



Ian. 30, 1951 R. J. TURNER TILTING BREECH BOLT LOCK ACTUATING MECHANISM2 Sheets-Sheet 1 Original Fild Jan. 3, 1942 E WM RN MN Jan. 30, 1951 VJ. TURNER TILTING BREECH BOLT LOCK ACTUATING mscx-mmsm 2 Sheets-Sheet 2Original Filed Jan. 5, 1942' Patented Jan. 30, 1951 TILTING BREECH BOLTLOCK ACTUATING MECHANISM Russell J. Turner, Butler, Pa. Originalapplication January 3, 1942, Serial No. 7 425,541. Divided and thisapplication June 15,

1944, Serial No. 540,404

16 Claims.

This invention relates generally to firearms and more particularly tobreech loading gas-operated automatic firearms.

This is a division of the application on which United States LettersPatent No. 2,365,142 was granted on December 12, 1944, for Firearms.

This invention may be conveniently applied to all types of full andsemi-automatic firearms such as machine guns, heavy rifles, lightcarbines, automatic pistols and other similar self or automatic loadingweapons.

The principal object of this invention is the provision of an accurateand rugged. automatic, firearm the structure of which is reduced to avery few number of parts making the firearm simple in construction andin operation and economical to manufacture.

Another object is the provision of an automatic firearm that may becompletely dismantled without the use of hand tools.

Another object is the provision of a breech loading gas-operatedautomatic firearm that employs the gas pressure of the charge to unlock,withdraw and open the breech, cock the piece, xtract and eject theshells, insert a fresh load from the magazine, lock the breech and firethe load.

' Another object the provision of a double stepped triggerthat convertsthe full automatic firearm into a semi-automatic firearm which requiresthe trigger to be pulled to fire each shot.

' Another object is the provision of an operating arm having a camsurface which locks the breechblock in its firing position and wheninitially retracted by gas pressure unlocks the breechblock bywithdrawing the cam surface from its operating position.

Another object is the provision of a novel link which connects theoperating .arm with the breechblock and serves to dislodge thebreechblock from its seat and slide it rearward1y to open the breech,cock the piece, and extract and eject the empty shell.

i Another object is the provision of a'novel firing pin and an extensionon the breechblock connecting-link which prevents the firing pin fromengaging the primer unless the breechblock'is fully locked in its closedposition. V

Another object is the provision of a shoulder in -t-he side of thereceiver against which the breechblock maybe seated and locked in "itsclosed position:-

Another object is the which is tightly closed when the breechblock is,locked-in the firing position and is opened in-v stantaneously when theempty shell is ejected through an opening in the operating arm when inits retracted position.

Other objects and advantages appear in the following description andclaims.

In the accompanying drawings a light semiautomatic carbine is employedas a practical embodiment to illustrate the principles of this in-.vention wherein:

Fig. 1 is a top plan view of the firearm with parts in section and partsbroken away, showing the breechblock inits retracted position.

Fig. 2 is a view similar to Fig. 1 showing the breechblock in its closedand fully locked position.

Fig. 3 is an enlarged transverse sectional view illustrating thebreechblock and operating link in the position shown in Fig. 2 withparts broken away.

Fig. 4 is a side elevation of the operating arm and the breechblock withparts in section and parts broken away. 7 r

Fig. .5 is a top planview of the firing pin in the firing position withthe link illustrated in dotted lines.

Fig. 6 is a view similar to Fig. 5 illustrating the firing pin locked inits retracted position.

Fig. 7 is a perspective view of the under side of the link. 7

Fig. 8 is a side elevation of the hammer and trigger mechanism withparts broken away, illus trating the semi-automatic feature.

Fig. 9 is an enlarged view of a modified firing pm.

Fig. 10 is an enlarged view of the firing chamher with the breechblockpartially retracted from its firing position.

Referring to the drawings the body of the firearm comprises three parts,the barrel 10, the receiver or frame II and the grip or stock I2. Thebreech end l3 of the barrel is fitted to the front end of the receiverII and projects into the forward end of the receiver chamber 14. Thestock i2 is secured to the rear end of the receiver or frame I I. Theforward end of the receiver chamber I4 is open at the bottom to admitthe cartridge magazine l5. The right side of the receiver is providedwith opposed grooves It in a. longiprovision of a receiver tudinallyextending slot which extends for the full length thereof and whichslidably carry the action or operating arm ll. On the same side the rearportion of the receiver chamber I is closed by a removable cover plate18 which retains theoperating arm l1 and covers the hammer 20 and thetrigger mechanism 2|. By first 3 removing this cover plate the wholefirearm may be dismantled.

The breechblock 22 is arranged to slide longitudinally Within thereceiver chamber l4 and carries the firing pin 23. The front end of thebreechblock is recessed in the usual manner as indicated at 24 toreceive the rim and primer of the cartridge shell 25. The extractor claw26 is pivoted in the side of the breechblock and extends forwardly andinwardly to catch on the rim of the cartridge to extract it from thebreech of the barrel. An ejector 2? is fixed to the Wall of the chamberl4 and is arranged to strike the rim of the cartridge shell and swing ittoward the extractor claw when the breechblock is substantially fullyretracted. An aperture 28 is provided in the forward portion of theoperating arm H to permit the shell to be thrown out of the receiverchamber when the operating arm is in its retracted position.

In the left side at the front of the receiver chamber a pocket isprovided which tapers towards the breech from the beveled shoulder 3|.The corresponding side of the back of the breechblock is provided withthe beveled surface 32 which is complementary to and is received by theshoulder 35. When the breechblock is brought forward until the front endengages the end of the barrel it is then shoved sideways to seat thesurface 32 on the shoulder 3|. The front end of the breechblock is atthis time normal to the axis of the barrel and held tightlythereagainst.

The breechblock is shoved sideways into the pocket 3% by means of thecomplementary cam surfaces 33 and 34 at the rear ends of the operatingarm I 7 and the breechblock 22 respectively. The operating arm ispermitted more travel forward than the breechblock. When these twomembers are retracted to the rear of the receiver chamber 54 the camsurfaces 33 and 34 intermesh as illustrated in Figs. 1 and and theforward travel of the operating arm moves the breechblock forwardlythrough these cam surfaces until the front end of the breechblockengages the end of the barrel. The breechblock is stopped but theoperating arm continues to move forwardly and the cam surface 33 ridesup the cam surface 34 and shoves the rear end of the breechblock to theleft into the pocket 35. The breechblock is of such length that thebeveled surface 32 seats firmly on the shoulder 3i and is locked inplace by the cam surface 33 resting on the outermost surface of the cam34.

The complementary surfaces 3| and 32 are beveled to such a degree thatthe blowback of the recoil would unseat and force the breechblock to theback of the receiver chamber I 4 if it were not for the fact that thecam 33 locks the breechblock in its seated position.

The operating arm and the breechblock are operatively connected by thelink 35 which is provided with a depending stub shaft at each endthereof. The stub shaft 35 is journaled in a vertical opening in therear end of the operating arm and the stub shaft 3? is journaled in thevertical opening 39 which extends into the firing pin chamber of thebreechblock. The curved portion of the cam surfaces 33 and 34 are arcsstruck from the axis of the stub shaft 31 which eliminates anyinterference between the action of the cam surfaces and the action ofthe link. There is no play or clearance permitted between the link andits associated parts. Thus the operation of the cam surfaces and thelink are in phase which produces a smooth and uniform action.

A portion of the outer end of the stub shaft 3'! is cut away, leavingthe vertical cam face 38 which lies in a plane passing through the axesof the stub shafts 3.5 and 37. The end of the shaft 31 carrying the face38 extends within the firing pin bore and is received in the slot 40 cutin the upper surface of the firing pin 23. If the firing pin is largeenough in diameter a circular groove 40 may be employed in place of theslot 40 which would permit the firing pin 23 to rotate as shown in Fig.9. In the structure illustrated in Figs. 3 and 6 the firing pin isprevented from r0- tating because the end of the stub shaft 37 contactsor lies closely adjacent the bottom of the slot 45.

When the breechblock is seated and locked in the firing position asshown in Fig. 2 the longitudinal axis of the link 35 and the cam face 38is disposed parallel to the transverse shoulder 4| in the firing pinforming the back of the slot 40. In this position the shoulder 4| isspaced approximately five hundredths of an inch from the face 38 asillustrated in Fig. 5. This clearance provides ample movement for thefiring pin to discharge the primer of the cartridge for such movementmay be five hundredths of an inch or less. If the link 35 is swungthrough a few degrees the cam face 38 engages the shoulder 4| to retractthe firing pin 23 and prevent any forward movement thereof. Thusaccidental striking of the firing pin by the hammer 20, or any otherunforeseen object, prevents the firing pin from engaging the primerunless the breechlock is fully locked in its firing position with thelink 35 positioned at right angles to the axis of the gun. It will benoted from the enlarged view of Fig. 5 that it takes very littleswinging movement of the link 35 before the cam face 38 on the shaft 31engages the shoulder 4| of the firing pin. This firing pin safety thusbecomes effective before the breechblock is unlocked from its firingposition.

The firearm used for the purpose of illustrating this invention is ofthe semi-automatic type wherein the trigger mechanism is provided withan upwardly extending fork member 43 having opposed shoulders 44 and 45on the inner edges of the fork members. When the piece is being cockedby the breechblock sldiing rearwardly the hammer tongue 46, which isprovided with the shoulders 4'! and 48 complementary to the shoulders 44and 45, is inserted between the forked members of the trigger,permitting the shoulder 41 on the tongue to engage under the shoulder4.4 of the trigger befor the latter has been released after the firstfiring. As the trigger is released the shoulder 44 slides off theshoulder 4'! and the shoulder 45 engages the shoulder 4a on the hammertongue. When the trigger is pulled the shoulder 45 slides off theshoulder 48 and releases the hammer so that it is free to strike thefiring pin 23. Before the trigger can be released the shell is fired andejected and the hammer is recocked with the shoulder 41 again engagingon the shoulder 44. If the hammer shoulder 4'! did not engage thetrigger shoulder 44 while the trigger was still held back the firearmwould con,- tinue to shoot automatically.

Suitable safety means 50 are provided to lock the trigger mechanism 2|.

The fore end of the operating arm I! is provided with a knob 5| whichmay be grasped by the hand to retract the operating arm. Upon,

up a shell from the magazine 15 and inserts it into the breech of thebarrel. The piece is thus cocked loaded and ready to fire.

An actuating rod 52 is detachably connected at one end to the fore partof the operating arm ii and at its other end to the gas piston head 53which is arranged to operate within the gas cylinder 54. The rod 52 andthe operating arm I! are normally retained in the forward position bythe actuator spring 55 which is inserted under initial compressionbetween the piston head 53 and the actuator bracket 56. The latter issecured to the barrel and is provided with a slot for receiving theactuator rod 52.

The fore end of the gas cylinder 54 is provided with the enlarged head51, the peripheral surface of which is spherically ground to fit thespherically ground socket 58 in the gas cylinder block or support '60that is secured to theside of the barrel adjacent the outer end.

In operation when the gun is closed and empty, and a full magazinehasbeen inserted, the breechblock 22 is pulled all the way back by theknob 5| on the operating arm H, which action cooks the piece. The knobis then released and the actuator spring 55 moves the breechblockforward, picking up a round from the magazine and inserting into thebreech. Continued movement of the operating arm then locks thebreechblock in place. When the cartridge is fired the bullet travelsdown the barrel l and after it passes the gas vent 64 a portion of thepropellant gas blows back through the vent, filling the gas cylinderspace and driving the piston 53, the operating arm and the breechblockback to the end of their stroke. The initial movement of the operatingarm causes the two opposing cam surfaces 33 and 34 on the arm andbreechblock to slide relative to one another to unlock the breechblock.When the operating arm I! starts to the rear the link 35 is swungclockwise, causing the face 38 on the shaft 31 of the link to engage theshoulder 4! in the end of the slot 40 in the firing pin 23. The swingingof the link' draws the firing pin back from the forward end of thebreechblock and locks the same against forward movement. Any accidentalbreakage of the trigger mechanism causing the hammer to fall at the wrontime could not fire the gun. Thus the initial rearward movement of theoperating arm swings the link 35 which looks the firing pin andsimultaneously slides the cam surface 33 rearwardly of the cam surface34 until they intermesh as shown in Fig. 1 at which time the breechblockis completely unlocked. The cam surfaces 33 and 34 thus unlock thebreechblock independently of the link 35.

If a round has been fired the breech pressure a will force the unlockedbreechblock off the shoulder 3! and out of the pocket 3|]. The force ofthe breech pressure on the breechblock acts through the cam surfaces 34and 33 to aid the force, previously transmitted to the operating arm, inmoving the mechanism to the rear of the chamber. The link 35 takes nopart in the action of these forces other than to maintain the camsurfaces in contact during the complete operation.

If the breech is opened manually by drawing back the operating arm bymeans of the knob 5|, then the link 35 gradually withdraws the rear endof the breechblock from the pocket 30 and off the shoulder 3| as the camsurfaces 33 and 34 slide over one another andthe' breechblock iscompletely withdrawn from the pocket when these cam surfaces intermeshas shown in Fig. 1. Further retraction of the operating arm draws thebreechblock to the rear of the chamber. Under these conditions the linknot only functions to lock the firing pin but it also acts as a couplingto pull the breechblock out and back. When the knob 5| is released thespring drives the operating arm forward. The cam surface 33 forces thebreechblock forward, seats it and looks it by riding over the camsurface 34. The link 35 is not employed to transmit force to the blockduring this forward movement. 4

During the rearward stroke of the breechblockthe empty shell is carriedback by the extractor claw 26 until the rim of the shell hits theejector. 21 which throws the shell through the operating arm aperture 23and out of the gun. As the breechblock draws away from the breech theextractor claw withdraws the empty shell and carries it back until therim strikes the ejector, pivoting the shell on the extractor claw andswingtially fully retracted. During the rearward stroke the breechblockforces the hammer down, cans-- ing the shoulder 41 to engage under theshoulder 44 before the operator has a chance to release the trigger. Thebreechblock then strikes the rear Wall of the receiver chamber with theoperating arm. The actuator spring 55 is then fully compressed and thestored energy then moves the mechanism forward. Upon its forwardmovement the breechblock picks up another round from the magazine andinserts it into the breech. When the breechblock is stopped in itsforward travel by the barrel ID the continued pull of the actuatorspring 55 on the operating arm causes the link to rotatecounterclockwise and the two cam surfaces 33 and 34 slide upon oneanother, thus driving the end of the breechblock sideways into thepocket 30 and looking it on the seat 3|.

' When the operating arm ii is in the forward quick access to the hammerand position the aperture 23, through which the discharged shell isthrown, is forward of the receiver and any opening into the receiverchamber is closed against mud or sand or foreign matter that wouldordinarily fall into the mechanism. The time that the aperture 28 isopen during discharge is very short and the shell is on its way outduring most of this time. Thus the firearm is very well protected andwill continue to fire after being completely buried in mud. The coverplate l8 over the rear end of the receiver and back of which theoperating arm ll slides provides trigger mechanism.

I claim:

1. In a'firearm, the combination of a barrel, a receiver secured to thebarrel and provided with a, chamber, a breech block member mounted inthe chamber for longitudinal reciprocation therethe pocket and whichride .upon Lone vanother tw move' the rear end oftthei'breechablockimember away lfrom theoperating :armandeinto seating engagementaagai-nstjatheishoulderlinithe pocket whenthe I frontzendr of'ithebreech -;block.' .mem-

ber-is inengagement with the front'a'wall; of '..;the chamber.

2. fm =a. firearmf the combination of :a receiver,

a breech-block member and adspringebiased operatingarm'-'-memberreciprocallycarried w.IoyltheJreceiver, a pocket in thereceiver,eashoulder eat the'rear'end of the pocket facingeforwardlyaandoutwardly to-form:a seat;oontinuonslyeengaging and mating complementaryioverlappedzcamasurfaces of 1 reversed curvature;onizsai'dsmemberezinterengaged in; surfacelicontact to :transmitiblowback forces and :permit the springebiasedi. operating ar-m to move-:the'breechebeockito thei front or the receiver and -then slideoversoneaanother to seat and lock the breechblocki .memberain thefiring-positionin said po'cketgandz meansrtmactuateusaid-operating arm'cm'ember.

3." Ina firearm; the combinationtof -a receiver,

"a breech-block member i, and -an operating arm member reciprocallycarried by I the 1 receiver, :.a pocket in thereceiver; a shoulder atthe rearen'd of the pocket facing forwardlyand-outwardlyzto form" aseat,- continuously engaginge and .mating 'complementary cam surfaces:onesaid em'embers having reversed circular -arc .portionsinterengagedin surface-contact to transmit blow back 'forces and' movethe .breech-b1ock to the front 'of" the receiver and' thenslide overioneanother to seat arid lock the breechfiblock @member .inthe-firingposition in-said polzketaan'd a link :hav-

ing spaced stub shafts -pivotally -conn-ecting said members permittinglimited-relative zmovem'ent therebetween, said link pivoting on: thecenters from which-the cam surfaces are-generated.

=-4.- In a fi-rearm,- the combination of -a receiver,

: a"-breechb1ock rmember andan'operating arm member reciprocally:carried by the receiven- -a firing pin carriedmy the breechblockmembema pocket-in the receiver-,= a shoulder-iatthe rearwend 'ofthe' po'cket facing forward-ly and outwardlywto I 'fo'rm a seat;continuously 'engagingzand:imating complementary: camasurfaces eon-maid:members having i reversed:- circulararc po'r tions' 2;:interengaged:=i1rsu rface contact to transmiti.blow-back forces-and move" thebreech-'blockto the'front-of carried by said link for retracting andlocking the firing pin upon initial movement ofithezoperating'arm beforethe breech-block -;is.-un;locked from the firing position 5. In a,firearm, the combination of a'receiver,

.a breech-block member and an operating arm member reciprocally carriedby-thereceiver, a

:firing pin carried by the breech block, -:a pocket zinrone side ofthereceiver, a, shoulder at the rear end of thepocketlfacing forwardlyand outwardly to'form a seat, continuously engaging and .rmating.complementary. ,curved camsurfaces on said members havingreversedcircularearcgportions. interengaged in surface contact to .transemitblow back: forces when .thenembers are moved rearwardly of the pocket inthe receiver and which slide over one another, to seat and lock thebreech -b1ockmember in, thefiring posi- ;ti on do said nocket,-;a linkhaving spacedQstnb ;shafts mivetallv r onn ctine said mem s 1 munittinge mited relative, movement therebetween, :saiid linkrpivotingonthecenters from which the cam surfaces aregenerated, andmeans on thebreecheblQ-Qklink-shaft for retracting and locking :the gfiring (pinupon initial movement of the operating 1arin ,before the breech-block isunlocked, from, the firing position.

v.6. In-:a-;firearrn,;the combination of a receiver havingga chamber,a.; barrelsecured to the front end ;,of the receiver, a breech-blockslidably mounted .to; reciprocate longitudinally-within the ;chamber;aof the receiver, a pocket on one side 10ft the receiver chambertapering from adjacent the barrel, a shoulder at the 'rear end of ,thepocket facing forwardly and outwardly toward thercharrrbengazreciprdcating; breech-block operating. armgslidablygsupported:by thereceiver on .theppposite side ,of the chamber from the pocket, ;a linkhaving; spaced, stub shafts pivotally-connecting therearef,thetbreech-bloek with said .arm,iw ndrasurface-on;said operatingarm to transmit -,blow back forces and toengage and move the;,breech-lol o ck v forwardly and force the rear, end, thereof into the,;pocket and ,into seat- ,ing engagement with the shoulder, when thefront end of,,tl 1e,,breech-b1ock is in engagement with the front ,wallof the" receiver, in its firing positiong said linkwithdrawingthebreech-block from chamber, a reciprocating t breech-block operat- -;ing:arm slidably; supportedqby the, receiver ,on

Y the opposite side of the chamber from the pocket,

a.;linkyhaving spacedstub; shafts pivotally conneoting the rear of V,'the;,breech-b1ock with said .arm,- a--surface on said operating arm totrans- .imit blow; back forces and; to 'engageand move ,50'

gendthereofinto the -pocket and into seating en- ;gagement.-withthe-.shoulder-when the front end ofithe breech-block is ,;in-engagementwith the thQvbPChirb1QGk forwardlyand force the rear front-wall of .thereceiver in its firing position, said linkwithdrawing, the breech-blockfrom the shoulder andaetractinggit rearwardly in the receiver.chamber-when-saidoperating arm is reatracted-ra-nd means, on; ne rth ln e ubrshaft pivoted in the breech-block for holding theg-firingapin inI its retracted position when the operating arm. swings saidlink.

rIn afirearm ithe cornbination, of, a. receiver havingragchambemabarrel-secured togthe front end ofqthe receiver, ,aybreech-blockslidably mounted to reciproeate;longitudinally within- ;the ;chamberoffithe; receiver, a.firing,pin carried by the zbreechgblockma pocket.on. one side of the receiver g-chamber 1 tapering from. adjacent. the.barreL, a shouldergahthe rearend- .of, the pocket facing forwardly andoutwardly toward the chamber,,- av ;reqiprocating. breech-blockoperatills-z arm slidably supportedby the. receiver 'on t e oppo e,s eprthe-chamber from th ke 3 -5, he t p link vrn r a 'i eden nd n lsh f a e2 Jr, in:

Quo ed; in sa ar n-ana the other shaft pivotally mounted in thebreechblock, a surface on said operating arm arranged to transmit blowback forces and to engage and move the breech-block forwardly and forcethe rear end thereof into the pocket and into seating engagement withthe shoulder when the front end of the breech-block is in engagementwiththe front wall of the receiver in its firing position, said linkwithdrawing the breech-block from the shoulder and retracting itrearwardly in the receiver chamber when said operating arm is retracted,a shoulder on the firing pin, and a cam face on the link shaft in thebreech-block arranged to engage the shoulder on the firing pin toretract and hold it from firing when the operating arm swings said link.

9. In a firearm, the combination of a barrel, 7

a receiver secured to the barrel and provided with a chamber, abreech-block member mounted in the chamber for longitudinalreciprocation therein, a pocket in the receiver and tapering forwardlyto the barrel, a shoulder at the rear end of the pocket facing forwardlyand outwardly toward the chamber to form. a seat, an operating armmember for the breech-block mounted adjacent the opposite side of thechamber from the pocket, continuously engaging and mating, complementarycam surfaces on the members having reversed circular-arc portionsinterengaged to transmit blow back forces when the members are retractedrearwardly and which ride upon one another to seat and lock thebreech-block member when moved into the pocket, and a link having spacedstub shafts pivotally connecting said members permitting limitedrelative movement therebetween, said link pivoting on the centers fromwhich the cam surfaces are generated, the combined action of said camsurfaces and said link being arranged to force the rear end of thebreech-block member on the shoulder and lock it in firing position whenthe front end of the breech-block member is in engagement with the frontwall of the chamber and to unlock and retract the breech-block to' therear of the chamber.

10. In a firearm, the combination of a barrel, a receiver secured to thebarrel and provided with a chamber, a breech-block mounted forlongitudinal reciprocation in the chamber, an action arm arranged tolock the breech-block in the firing position, means defining a firingpin bearing disposed longitudinally in the breechblock, a firing pinoperable therein, means defining ,a second bearing disposed normally toand intersecting the firing pin bearing, a shoulder on the firing pinadiacent the second bearing, and means operated by said action arm andjournaled in the second bearing to swing and engage said shoulder andprevent the firing pin from operating as the action arm retracts.

11. The structure of claim 10, characterized in that said last mentionedmeans comprise a shaft having a notched section that permits movement ofthe firing pin when the breech-block is locked and engages said shoulderwhen the breech-block is unlocked.

12. In a firearm, the combination of a receiver, having a chamber, abarrel secured to the front end of the receiver, a breech-block slidablymounted to reciprocate longitudinally within the chamber of thereceiver, a forwardly and outwardly facing seat on one side of thereceiver chamber to be engaged by the breechblock when locked in firingposition, a reciprocating operating arm slidably supported by thereceiver, a bearing in the breech-block, a bearing carried by theoperating arm, a link having spaced depending shafts journaled in thebearings of the breech-block and the operating arm for retracting thebreech-block from said seat, and continuously engaging and matingcomplementary interengaging cam means of reversed curvature on thebreech-block and the operating arm for transmitting forces therebetweenand for seating and locking the breech-block on said seat. a p

13. The structure of claim 12 which also includes a firing pin carriedby the breech-block, a shoulder on the firing pin adjacent the bearingin the breech-block, and means on the shaft in said last mentionedbearing for preventing the operation of the firing pin when the linkswings before retracting the breech-block from said seat.

14. The structure of claim 12 which alsoincludes a firing pin carried bythe breech-block, means efiective by the rotation of the shaft in saidbearing for locking and unlocking the firing pm.

15. In an automatic firearm, the combination of a barrel. a receiversecured to the barrel and provided with a chamber, a breech-block membermounted in the chamber for longitudinal reciprocation therein, a pocketin the receiver and tapering forwardly to the barrel, a shoulder at therear end of the pocket facing forwardly and outwardly toward thechamber, an action arm member slidably mounted in the receiver on theside opposite to the pocket, continuously en- ;gaging and matingcomplementary cam surfaces on the members having reversed circulararcportions interengaged in surface contact to transmit forces therebetweenwhen the members are retracted rearwardly of the pocket, the curvedportion of the cam surface on the action arm member being positionedbehind the curved cam surface on the breech-block member when retracted,the curved cam surfaces riding upon one another to force the rear end ofthe breechblock member into the pocket and into seating engagement withthe shoulder when the front end of the breech-block'member is inengagement with the front wall of the chamber and when on top of oneanother to lock the breechblock member in firing position. and a linkpivotally connect d to each of said members on center points from whichthe convex portions of said cam surfaces are enerated to continuouslymaintain the cam surfaces in contact.

16 The structure of claim 15 which also in cludes a firing pin carriedby the breech-block,

and means actuated by the swinging movement of the link to retract thefiring pin when the action arm member is unlocking the breechblockbefore it is unseated.

RUSSELL J. TURNER.

REFERENCES CITED The fo lowing references are of record in the file ofthis patent:

UNITED STATES PATENTS Num er Name Date 289.972 Burgess Dec. 11, 1883317,162 Maxim May 5, 1885 544.657 Browning Aug. 20, 1895 545,672Browning Sept. 3, 1895 (Other references on following page) Number 11UNITED STATES PA'I'ENTS Name Date Browning Feb. 22, 1898 Mannlicher May19, 1903 Freeman May- 30, 1905 Bernard Oct. 31, 1905 Mauser Dec. 17,1912 Osborne Oct. 28, 1913 Swebilius et a1. Mar. 28, 1916 Number 1.2Name Date Squire et a1 Sept. 30, 1919 Cox Oct. 12, 1920 Horan Jan. 9,1923 Fearn July 10, 1923 Holek Sept. 1, 1931 Browning Apr. 9, 1940 HoranFeb. 15, 1944

